THE MICROVASCULAR HYPEREMIC RESPONSE TO OCCLUSIVE OR PARTIAL BLOOD FLOW RESTRICTION

Brianna N. Cupp, Daphney M. Stanford, Matthew A. Chatlaong, Matthew B. Jessee. The University of Mississippi, University, MS. BACKGROUND. Blood flow restriction (BFR) alone decreases muscle atrophy following immobilization. It is unknown what effect BFR alone has on microvasculature. The purpose of this study is to determine the acute effect of BFR alone on oxygen extraction rate (Slope 1, S1) and reactive hyperemia (Slope 2, S2) when compared to a protocol known to improve vascular function. METHODS. 9 females and 11 males (height: 164.2±21.1 cm; weight: 72.7±29.0 kg; age: 27.6±10.6 y) completed 3 protocols (separate visits), on the right arm, while supine. For all conditions a cuff was secured on the upper arm. First, after a 5min rest, AOP was measured. After another 5min rest, the protocol started. For control (CON), the cuff remained deflated. For BFR, a cuff was inflated to 80% arterial occlusion pressure (AOP) for 5 cycles (5min inflation/3min deflation). For ischemic preconditioning (IPC), a cuff was inflated to 105% AOP for 4 cycles (5min inflation/5min deflation). A near-infrared spectroscopy device (NIRS) continuously estimated deoxy(Hb, µM∙s-1)/oxy(O2,µM∙s-1) heme and tissue saturation index (TSI, %∙s-1) at the forearm. S1 was the 60s following cuff inflation and S2 was the 30s immediately after cuff deflation. The regression slopes from each cycle were averaged and compared across conditions with Bayesian RMANOVA. Results presented as mean±SD. BF10=likelihood of the best model vs the null. RESULTS. S1 for TSI (Condition: BF10=4.518e+13) was steeper in BFR (-0.07±0.04) when compared to CON (0.01±0.01; BF10=202810.265), but flatter than IPC (-0.10±0.03; BF10=7.330). IPC was steeper compared to CON (BF10= 1.524e+8). S1 for O2 (Condition: BF10=6.682e+11) was positive and steeper in BFR (0.17±0.11) than CON (0.01±0.01; BF10=24409.937) and IPC (-.05±0.07; BF10=407178.004). IPC was negative compared to CON (BF10=32.242). S1 for Hb (Condition: BF10=3.856e+22) was positive and steeper in BFR (0.21±0.05) than CON (-0.01±0.0; BF10=4.626e+10) and IPC (0.15±0.05; BF10=226.453). IPC was positive compared to CON (BF10=3.097e+9). TSI for S2 (Condition: BF10=7.977e+15) was steeper for BFR (0.76±0.30; BF10=1.495e+7) and IPC (1.06±0.39; BF10=3.947e+7) compared to CON (0.0±0.01). BFR was typically flatter than IPC (BF10=42.285). CONCLUSION. The current data suggests BFR has a lower extraction rate and hyperemic response than IPC. Chronic application of BFR alone may elicit vascular adaptations, but the magnitude may be lower than IPC

ACUTE HYPEREMIC RESPONSE TO BLOOD FLOW RESTRICTION AND ISCHEMIC PRECONDITIONING PROTOCOLS

Daphney M. Stanford, Brianna N. Cupp, Matthew A. Chatlaong, Matthew B. Jessee. University of Mississippi, Oxford, MS. BACKGROUND: Ischemic preconditioning (IPC) typically improves vascular health, but it is unknown if a non-ischemic protocol would have a similar acute stimulus. The purpose of this study was to compare the acute hyperemic response of IPC and blood flow restriction (BFR). METHODS: 20 subjects (45% female) completed 3 conditions over 3 visits (randomized and counterbalanced). While supine, a pneumatic cuff was placed on the upper right arm, and following 5min rest, arterial occlusion pressure (AOP, mmHg) was measured, then following a second 5min rest the protocol started. For IPC, a cuff inflated (105%AOP) for 5min with 5min of rest for 4 cycles. For BFR, a cuff inflated (80%AOP) for 5min with 3min rest for 5 cycles. CON had a deflated cuff on for 40min. Using duplex ultrasound distal to the cuff, brachial artery blood velocity (cm/s) and diameter (cm) were recorded at baseline (Pre) and after cuff deflation. The first 30s of blood velocity after cuff deflation was averaged, and the last 30s of artery diameter after cuff deflation was averaged. AOP was measured immediately after (Post) the protocol. Discomfort (DIS, A.U.) was asked with a 0-10 scale at Pre and Post. Changes in artery diameter and blood velocity (last cycle-Pre), and changes in AOP and DIS (Post-Pre) were compared across conditions using Bayesian repeated measures ANOVAs. Results presented as mean±SD. BF10=likelihood of the best model vs the null. RESULTS: The change in artery diameter (Condition: BF10=400.697) for BFR (.01±.02) was higher than CON (-.01±.02; BF10=2.651), and lower than IPC (.02±.03; BF10=1.569). IPC was higher than CON (BF10=82.853). The hyperemic response (Condition: BF10=5.887e+15) for BFR (6.7±7.3) was higher than CON (-3.1±5.1; BF10=148.630), and lower than IPC (34.2±14.2; BF10=156409.519). IPC was higher than CON (BF10=3.128e+7). The change in AOP (Condition: BF10=1.296) was higher in BFR (-8.95±10.83) when compared to CON (-2.26±9.69; BF10=1.268), but similar to IPC (-6.53±5.81; BF10=.345). IPC and CON were similar (BF10=.576). The change in DISC (Condition: BF10= 19526.876) was higher in BFR (4.08±2.6) when compared to CON (1.3±2.1; BF10=195.289), but similar to IPC (4.03±2.63; BF10=.244). IPC was higher than CON (BF10=141.363). CONCLUSION: Individuals may want to implement bouts of IPC instead of BFR for vascular health because the acute stimulus is stronger while the discomfort is similar between protocols

Application of Nuclear Magnetic Resonance and Hybrid Methods to Structure Determination of Complex Systems

The current main challenge of Structural Biology is to undertake the structure determination of increasingly complex systems in the attempt to better understand their biological function. As systems become more challenging, however, there is an increasing demand for the parallel use of more than one independent technique to allow pushing the frontiers of structure determination and, at the same time, obtaining independent structural validation. The combination of different Structural Biology methods has been named hybrid approaches. The aim of this review is to critically discuss the most recent examples and new developments that have allowed structure determination or experimentally-based modelling of various molecular complexes selecting them among those that combine the use of nuclear magnetic resonance and small angle scattering techniques. We provide a selective but focused account of some of the most exciting recent approaches and discuss their possible further developments